navigation
Like signs in a building that point to rooms, it controls which screen the app shows and how people move between them.
Think of the signs and hallways in an office that guide you from the lobby to a meeting room. In an app, navigation is the set of rules that decides which screen appears and how to get to another one.
It matters because people need a clear path: opening the home screen, tapping a tab, going to details, and getting back. It also handles deep links, which are special links that open a specific screen inside your app.
In practice you define a stack, which is a list of screens with a back trail, or tabs, which are a row of buttons for main sections. Buttons and links trigger moves, and you can pass a small value, like an id number, to the next screen.